This invention relates generally to screw fasteners, and, more particularly, to screw fasteners assemblies of the kind that captivate a screw in a housing.
Captive screw assemblies of this particular kind have been in common use for preventing the full removal of screws from the housings or other parts in which the screws are contained. These assemblies typically call for using reduced shank diameter blanks or screws without threads, which are installed in holes formed in the appropriate housing. The blank is then captivated within the housing by thread-rolling threads on the blank, such that the major diameter of the threads is larger than the diameter of the housing hole in which the blank is placed. These captive screw assemblies are sometimes provided with a coil spring encircling the screw shaft. The spring is compressed when the screw is rotated in one direction and thus urges the screw head outwardly.
Captive screw assemblies of the type briefly described above, although generally effective, are not entirely satisfactory. The threads on the screw can only be rolled after the screw has been placed in the hole of the housing. This increases the cost of captive screw assemblies, because standard prethreaded screws cannot be used and because additional machinery and effort are ordinarily required to thread the blanks after they have been installed in the housing hole. Furthermore, reduced shank diameter blanks, which are later thread-rolled, are generally not as strong as prethreaded, full shank diameter screws made of the same material. In addition, such thread-rolled screws cannot readily be removed from the housing and replaced with another screw, if the need should ever arise.
It should, therefore, be appreciated that there is a need for a captive screw assembly which overcomes the above problems. The assembly should ideally utilize a conventional, prethreaded screw for strength and cost efficiency. The present invention provides the necessary solution.